This invention concerns a braking installation for a motor vehicle, said installation comprising a master cylinder controlled by a brake pedal and connected to feed circuits for the wheel brakes, as well as a hydraulic unit comprising brake fluid pressure pumps, these pumps being connected to the wheel-brake feed circuits and controlled by a computer.
In such an installation, braking is controlled primarily by the driver of the vehicle using the brake pedal which is connected to the pistons of the master cylinder by a pneumatic brake booster, the action of the driver on the brake pedal causing the vehicle to brake.
The operation of the brake fluid pressure pumps is controlled by the wheel traction control, wheel antilock and drive stability control computer, the computer controlling both the pumps and solenoid valves assembled in the wheel-brake feed circuits, in order to act selectively on one and/or the other of the wheel brakes of the vehicle.
Furthermore, the document FR 2 645 816 makes reference to a braking system comprising a master cylinder and remote brake fluid reservoir.
In these installations, a brake fluid reservoir is conventionally attached to the master cylinder and communicates with each of its chambers via brake-fluid feed and return conduits, the pistons of the master cylinder being fitted with conduits and brake-fluid valves. This known arrangement has the drawback of permitting travel and increasing the number of components in the master cylinder.
This invention is particularly intended to resolve these drawbacks in the prior art.
It concerns an installation of the type detailed above, whose master cylinder has a structure that is more simple than in the prior art and comprises fewer components and in which the travel is eliminated or at least reduced.
Accordingly, it provides a braking installation for a motor vehicle, comprising a brake fluid reservoir, a master cylinder controlled by a brake pedal and connected to feed circuits for wheel brakes, and a hydraulic unit comprising brake fluid pressure pumps, connected to the wheel-brake feed circuits and controlled by a computer, said installation being characterized in that the brake fluid reservoir is linked to said pumps by the first solenoid valves controlled by the computer and that it is separate from the master cylinder.
Thanks to the invention, it is no longer necessary to provide conduits or valves for brake fluid in the pistons of the master cylinder whose structure is considerably simplified.
This makes it possible to reduce or eliminate travel in the master cylinder and to install the reservoir remotely on the master cylinder, advantageously on the aforementioned hydraulic unit.
The reservoir is linked to the pumps of the hydraulic group directly without passing via the master cylinder, which makes it possible to increase the flow rate of the brake fluid supplying the pumps, to reduce the pressurization time in the wheel-brake feed circuits, and also to reduce the spurious noise related to the transfer of brake fluid to the pumps in the hydraulic unit.
According to another feature of the invention, the second solenoid valves controlled by the computer are assembled in the wheel-brake feed circuits between the master-cylinder outputs and the pump outputs.
This feature makes it possible to isolate the master cylinder of the hydraulic unit during operation of the hydraulic-unit pumps, such that the pressurization of the brake fluid in the wheel-brake feed circuits caused by operation of the pumps, does not affect the master cylinder, thanks to the closure of the second solenoid valves, and consequently it is not felt in the pedal.
These second solenoid valves are open in idle position to enable application of the brakes from the master cylinder and are closed by the computer, when the hydraulic unit is working.
Non-return valves are fitted in parallel on the second solenoid valves to prevent the backflow of brake fluid from the wheel brakes to the master cylinder.
In a first embodiment of the invention, the aforementioned first solenoid valves connect the reservoir to the inlets of the hydraulic-unit pumps.
Potentially, a calibrated orifice and a non-return valve, connected to each other in parallel are assembled in the conduits linking the reservoir to the pump inlets.
In an alternative embodiment of the invention, the first solenoid valves link the reservoir to the pump outputs whose inlets are linked to the reservoir via conduits comprising non-return valves preventing the passage of brake fluid towards the reservoir.